If you notice that your iPod Touch no longer stays charged for very long, even at a full charge, it could be that you are either running too many things at the same time, or that you need to replace the battery. Charge your iPod Touch and close down anything that you aren’t using and see if the charge holds longer. If not, then getting a battery replacement is your next best option.
To keep your battery running for its full life span, make sure not to overcharge it and avoid charging it unless it is at a 20% or less charge.